Field of the Invention
The present invention relates to a tool for removing damaged fasteners, and more particularly to a bit for removing damaged screws.
Description of the Prior Art
Screws are widely used fasteners with a driving groove, via which, the screws can be rotated by a screwdriver. However, the driving groove of the screws may be damaged due to many reasons, for example, user's overexertion during rotation, screwdriver doesn't fit the size or shape of the driving groove. Once the driving groove is broken or damaged, the screw can not be rotated by an ordinary screwdriver anymore, and can only be removed by a professional bit which is particularly designed to remove damage screws.
FIG. 1 shows a conventional bit 10 for removing a damaged screw A, wherein the bit 10 includes a head portion 11 and a shaft portion 12. The head portion 11 is sequentially provided with a front end section 111, a shrinking neck section 112 and a reversely threaded section 113. The front end section 111 is provided with two scraping edge 114. The shrinking neck section 112 is located between the front end section 111 and the reversely threaded section 113. The diameter of both ends of the shrinking neck section 112 is smaller than that of the front end section 111 and the diameter of the connection between the reversely threaded section 113 and the shrinking neck section 112, so that the front end section 111, the shrinking neck section 112 and the reversely threaded section 113 define a recess 115. The reversely threaded section 113 is connected to the shaft portion 12, and the thread of the reversely threaded section 113 is a reversely thread with respect to the thread of the damaged screw A, namely the reversely threaded section 113 rotates in a reverse direction with respect to the thread of the damaged screw A. The bit 10 can use the scraping edges 114 to dig into the driving groove A1 of the damaged screw A, then the bit 10 keeps rotating to make the reversely threaded section 113 bite into and unscrew the damaged screw A.
This bit 10 is able to remove the damaged screw A. When the bit 10 rotates, the two scraping edges 114 firstly cut into the damaged driving groove A1 (namely, the scraping edges 114 are mainly responsible for scraping operation), then the reversely threaded section 113 bits into the driving groove A1 which has been scraped, and the reversely threaded section 113 is responsible for screwing into and driving the bit to move forward. Due to the fact that the scrapping edges 114 are separated from the reversely threaded section 113 by the shrinking neck section 112, the two scraping edges 114 only extend to he shrinking neck section 112, and the reversely threaded section 113 is located behind the shrinking neck section 112, the scraping operation performed by the scrapping edges 114 will stop before the shrinking neck section 112, and the cutting operation performed by the reversely threaded section 113 starts only after the shrinking neck section 112. Therefore, the shrinking neck section 112 becomes an idle rotation section or period (during which no scraping operation is performed) when the bit 10 is screwing in the damaged screw A, as a result, the reversely threaded section 113 will bear extremely large resistance.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.